Laravel：身份验证每次都失败

I have created an app with the Laravel framework. I would like to use the built-in Laravel auth system. I have a quite strange problem with it. It always returns false when I try to log a user in with:

if (Auth::attempt(['email' => $email, 'password' => $password]))
{
    Log::info('User logged in'); 
}

I am sure the email and password given are correctly registered in the MySQL table which is named mD.

In the app/config/auth.php, I have correctly set the right table that I use to store users.

'table' => 'mD'

I also have correctly created required columns for this table (updated_at, created_at, remember_token).